Monolithically framed pellicle membrane suitable for lithography in the fabrication of integrated circuits

ABSTRACT

Monolithic framed pellicle membrane integrating a structural framing member with a membrane spanning the framing member. The monolithic frame pellicle membrane is suitable as an overlay of a reticle employed in lithography operations of integrated circuit manufacture. A semiconductor-on-insulator (SOI) wafer may be machined from the backside, for example with a bonnet polisher, to form a pellicle framing member by removing a portion of a base semiconductor substrate of the SOI wafer selectively to top semiconductor layer of the SOI wafer, which is retained as a pellicle membrane. In some exemplary embodiments suitable for extreme ultraviolet (EUV) lithography applications, at least the top semiconductor layer of the SOI wafer is a substantially monocrystalline silicon layer.

CLAIM OF PRIORITY

This application is a continuation of, and claims the benefit ofpriority to, U.S. patent application Ser. No. 16/832,456, filed on Mar.27, 2020 and titled “MONOLITHICALLY FRAMED PELLICLE MEMBRANE SUITABLEFOR LITHOGRAPHY IN THE FABRICATION OF INTEGRATED CIRCUITS,” which isincorporated by reference in entirety.

BACKGROUND

Demand for higher performance integrated circuits (ICs) in electronicdevice applications has motivated increasingly dense transistorarchitectures. With the continued scaling of the physical dimensions ofdevice features, such as transistor gates, gate contacts, and metalinterconnects, nanolithography is a key enabling technology. Achievingfeature dimensions in the 20-30 nm range may require extreme ultravioletlithography (EUV or EUVL) technology using the 13.5 nm EUV centerwavelength (13.3-13.7 nm band).

In the manufacture of ICs, substrate patterning employs lithographicmasks, referred to as reticles. Reticle patterns should have minimaldefects for highest device yields. Even in state-of-the-art cleanrooms,it is challenging to prevent minute particles present in the environmentfrom depositing on masks during storage and usage in lithographyequipment. Pellicles are typically attached to a reticle to avoidparticles from becoming a printable adder to the reticle pattern. FIG. 1depicts exploded and collapsed isometric views of a pellicle and frameassembly 100 further assembled with a reticle 115, in accordance withconvention. Assembly 100 includes a pellicle membrane preform 105attached to a pellicle frame preform 110. Assembly 100 is furtherattached to reticle 115 in a pelliclized reticle assembly 101, which issuitable for use in lithography operations of high volume ICmanufacture. Reticle 115 includes a printable pattern 130. In thisexample printable pattern 130 is a reversed image of what is to beprinted, which is typical of an EUV reticle that relies on reflective,rather than transmissive, optics.

Pellicle frame preform 110 is often made of a rigid bulk material suchas anodized aluminum or ceramic, and has a z-thickness T1 of 2-6 mm,typically set to be the same thickness as a reticle blank. During use,particles that happen to deposit on the pelliclized reticle assembly 101fall onto pellicle 105 (or the back side of the reticle), and aretherefore several millimeters away from the plane of printable pattern130 that is imaged. With the small depth-of-field of the optical system,such particles are out of the focal plane and do not alter a patternimaged upon an IC workpiece.

Pellicle membrane preform 105 has evolved with successive lithographygenerations as the emission wavelengths employed in the imaging processhave become shorter. Whereas generations ago, pellicle membrane preform105 was around 1 μm in thickness, thicknesses of 20-50 nanometer (nm)are typical for EUV systems. Such thicknesses pose an even greaterchallenge in view of the large area pellicle membrane preform 105 is tospan, which may be 100-150 mm×100-150 mm. For EUV systems, pelliclemembrane preform 105 typically has a polysilicon core or a carbon core.Polysilicon-core examples may have a variety of capping layercombinations. Carbon-core examples include graphene membranes orgraphite sheets, which may also be capped with a variety of materials.

To form assembly 100, pellicle membrane preform 105 is first fabricatedand then transferred to pellicle frame preform 110. Yield lossesassociated with fabrication steps such as separating and transferringthe thin, large area membrane are significant and thus currently resultin high unit cost per piece part, and low availability/supply.Additionally, as illustrated in FIG. 1, pellicle frame preform 110 istypically itself an assembly of multiple individual parts (e.g.,flexures 120, which couple to reticle studs 125). Each of these partspresent fabrication challenges, and all have yield losses associatedwith both their discrete manufacture and their integration into assembly100. In aggregate, these issues translate into the cost of a singlepellicle assembly 101 being in the tens of thousands of dollars.Considering the number of assemblies needed for each IC device product,and their finite lifetimes owing to the inherent fragility of eachassembly, pellicle assembly costs can be a significant factor in theunit cost of a IC device.

Pellicles and pelliclized reticle assemblies and their methods offabrication that can address one or more of the above issues wouldtherefore be commercially advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS

The material described herein is illustrated by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, elements illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some elementsmay be exaggerated relative to other elements for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements. In thefigures:

FIG. 1 depicts exploded and collapsed isometric views of a reticle witha pellicle and frame assembly, in accordance with convention;

FIG. 2A-2B are flow diagrams illustrating methods of fabricating amonolithic framed pellicle, in accordance with some embodiments;

FIG. 3A illustrates an isometric view of a monolithic framed pellicledelineated within a semiconductor on insulator (SOI) wafer from which itis machined, in accordance with some embodiments;

FIG. 3B is a cross-sectional view of a monolithic framed pellicleworkpiece evolving to include backside and front-side material layers,in accordance with some embodiments;

FIG. 4A is a cross-sectional view of a monolithic framed pellicleworkpiece being machined from the back side with a bonnet polisher, inaccordance with some embodiments;

FIGS. 4B, 4C and 4D illustrate cross-sectional views of a monolithicframed pellicle workpiece evolving to include a machined pelliclestructural frame, in accordance with some embodiments;

FIG. 4E illustrates a plan view of a monolithic framed pellicleworkpiece, in accordance with some embodiments;

FIG. 4F illustrates a cross-sectional view of a monolithic framedpellicle workpiece including backside features, in accordance with someembodiments;

FIG. 5 illustrates a monolithic framed pellicle, in accordance with someembodiments; and

FIG. 6 is a cross-sectional view of a pelliclized reticle assembly, inaccordance with some embodiments.

DETAILED DESCRIPTION

One or more embodiments are described with reference to the enclosedfigures. While specific configurations and arrangements are depicted anddiscussed in detail, it should be understood that this is done forillustrative purposes only. Persons skilled in the relevant art willrecognize that other configurations and arrangements are possiblewithout departing from the spirit and scope of the description. It willbe apparent to those skilled in the relevant art that techniques and/orarrangements described herein may be employed in a variety of othersystems and applications other than what is described in detail herein.

Reference is made in the following detailed description to theaccompanying drawings, which form a part hereof and illustrate exemplaryembodiments. Further, it is to be understood that other embodiments maybe utilized and structural and/or logical changes may be made withoutdeparting from the scope of claimed subject matter. It should also benoted that directions and references, for example, up, down, top,bottom, and so on, may be used merely to facilitate the description offeatures in the drawings. Therefore, the following detailed descriptionis not to be taken in a limiting sense and the scope of claimed subjectmatter is defined solely by the appended claims and their equivalents.

In the following description, numerous details are set forth. However,it will be apparent to one skilled in the art, that the presentinvention may be practiced without these specific details. In someinstances, well-known methods and devices are shown in block diagramform, rather than in detail, to avoid obscuring the present invention.Reference throughout this specification to “an embodiment” or “oneembodiment” means that a particular feature, structure, function, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “in an embodiment” or “in some embodiments” in various placesthroughout this specification are not necessarily referring to the sameembodiment of the invention. Furthermore, the particular features,structures, functions, or characteristics may be combined in anysuitable manner in one or more embodiments. For example, a firstembodiment may be combined with a second embodiment anywhere theparticular features, structures, functions, or characteristicsassociated with the two embodiments are not mutually exclusive.

As used in the description of the invention and the appended claims, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willalso be understood that the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items.

The terms “coupled” and “connected,” along with their derivatives, maybe used herein to describe functional or structural relationshipsbetween components. It should be understood that these terms are notintended as synonyms for each other. Rather, in particular embodiments,“connected” may be used to indicate that two or more elements are indirect physical, optical, or electrical contact with each other.“Coupled” may be used to indicated that two or more elements are ineither direct or indirect (with other intervening elements between them)physical or electrical contact with each other, and/or that the two ormore elements co-operate or interact with each other (e.g., as in acause and effect relationship).

The terms “over,” “under,” “between,” and “on” as used herein refer to arelative position of one component or material with respect to othercomponents or materials where such physical relationships arenoteworthy. For example in the context of materials, one materialdisposed over or under another may be directly in contact or may haveone or more intervening materials. Moreover, one material disposedbetween two materials may be directly in contact with the two layers ormay have one or more intervening layers. In contrast, a first materialor material “on” a second material or material is in direct contact withthat second material/material. Similar distinctions are to be made inthe context of component assemblies.

As used throughout this description, and in the claims, a list of itemsjoined by the term “at least one of” or “one or more of” can mean anycombination of the listed terms. For example, the phrase “at least oneof A, B or C” can mean A; B; C; A and B; A and C; B and C; or A, B andC.

In accordance with some embodiments herein, a monolithic framed pelliclemembrane integrates a structural framing member with a membrane spanningthe framing member. The monolithic frame pellicle membrane is suitableas an overlay of a reticle employed in lithography operations ofintegrated circuit manufacture. The term “monolithic” is used herein inthe context of the a framed pellicle membrane to mean both the membraneand the structural frame are of a single, contiguous starting substratecomprising at least a first material layer, that is to become themembrane, and a second material layer that is to become the frame. Asdescribed further below machining from a contiguous starting materialoffers significant advantages over separately preforming a discretemembrane material and a discrete frame material and then assembling thediscrete components together.

As described below, both material layers of the monolithic framedpellicle may have substantially the same chemical composition, withperhaps only a minority impurity dopant concentration differing betweenthe material layers. In some embodiments, both the frame material andthe membrane material are single crystalline. In some such embodiments,both the frame material and the membrane material have the samecrystallinity, are of the same crystal orientation, and of substantiallythe same composition, such that the both the membrane and frame are of asingle piece, or monolith, of crystal.

As further described below, a monolithic starting workpiece may be asemiconductor-on-insulator (SOI) substrate, which is subtractivelymachined, for example from the back side, to define a structural framethat is dimensioned to attach to a perimeter of a reticle, and to standoff a front side of the SOI workpiece by at least a few millimeters. Insome exemplary embodiments suitable for extreme ultraviolet (EUV)lithography applications, at least the top crystalline material layer ofthe SOI wafer is silicon. Although all embodiments leverage thecrystallinity and the monolithic nature of an SOI material, someembodiments may further leverage semiconducting properties of an SOIsubstrate, for example as a means of controlling electrostatic chargeand/or as a means of integrating sensory devices into the monolithicframed pellicle.

As further described below, a CNC bonnet polisher may be employed tomachine the SOI workpiece into a pellicle framing member by removing aportion of a base crystalline substrate material layer of the SOI wafer.Such back side processing may further comprise removing one or morematerial layers from the SOI wafer selectively to an insulator layer ofthe SOI wafer to ensure the precise thickness of the top crystallinelayer of the SOI wafer is fully retained as a pellicle membrane. One ormore thin films may be deposited over a front side of the SOI wafer toprepare the monolithic structure for use as a pellicle in an EUVenvironment.

Methods described herein generally entail processing a monolithicworkpiece comprising a substantially monocrystalline membrane materiallayer over a substantially monocrystalline frame material layer with anintervening material layer therebetween. When practicing the methodsdescribed herein, the monolithic workpiece may be mounted to a carrierwith a front side of the first material layer facing the carrier. Whilemounted, a recess may be subtractively machined into the second materiallayer with a remainder of the second material layer framing a perimeterof the recess. A membrane spanning the recess may be formed from thefirst material layer by the exposing a back side of the interveningmaterial layer with an etchant that removes the second materialselectively from the intervening material. The intervening materiallayer may therefore have any composition suitable for serving as a etchstop ensuring the uniform thickness of the first material layer isretained as an optimal membrane thickness of high strength and lowabsorbance.

FIG. 2A-2B are flow diagrams illustrating methods 200 for fabricating amonolithic framed pellicle, in accordance with some embodiments. Methods200 provide illustrative examples that may be readily modified withinthe scope of the broader techniques specifically demonstrated. In someembodiments, methods 200 begin with an input 205 where a commerciallyavailable SOI wafer is received. The SOI wafer may have any diametersufficient for the pellicle frame dimensions with some examples being200 mm, 300 mm, or even 450 mm. In some embodiments, the wafer receivedis a semiconductor-on-insulator (SOI) wafer having a top material layerthat is referred to herein as the “membrane” material layer as it is tobecome the pellicle membrane.

In exemplary embodiments, the membrane material layer is predominantlysilicon that is of a predetermined thickness suitable for a pelliclemembrane. In some advantageous embodiments, at least the membranematerial layer is a substantially monocrystalline (CZ) silicon (i.e.,substantially pure silicon) with only a minority concentration of one ormore impurities. Single crystal silicon membrane material isparticularly advantageous for EUV embodiments because monocrystallinesilicon has a favorably low absorption coefficient within the EUVemission band (e.g., <0.0015 at 13.5 nm). With the low absorptioncoefficient, a silicon single crystal pellicle membrane can havetransmission of 95%, or more, as a function of thickness. In comparison,polycrystalline silicon has a higher absorption coefficient such thatpolycrystalline silicon membranes may achieve only ˜82% transmissionvalue even at thicknesses of only 20 nm. Noting that EUV systems areentirely reflective such that imaging radiation must pass through apellicle membrane twice, transmission rates are compounded (e.g., with82% transmission then translating to a loss of −43% of incident EUVimaging radiation). Hence, the level of membrane transmission isimportant as a loss of transmission can significantly reduce throughputof a EUV imaging system.

Relative to polysilicon, single crystal silicon also has lowerdefectivity, significantly lower surface roughness, and intrinsicallyhigher mechanical strength than polycrystalline silicon (as shown inTable 1.)

TABLE 1 Single crystal Silicon Polysilicon Yield strength (GPa) 2.8-7  1.21 Density (kg/m3) 2330 2320 Young's Modulus (GPa) 62-202 120-203A single crystal silicon membrane should therefore be less subject tofailure mechanisms associated with EUV scanner exposure. In someexemplary embodiments, a single crystal silicon membrane layer has athickness less than 200 nm, and more particularly in the range of 15-150nm. Thinner membranes offer the advantage of higher transmission. Thelower thickness threshold of single crystalline silicon is below that ofpolycrystalline and amorphous films, which more readily suffer theformation of pinholes as thicknesses are reduced. However, due to itshigh EUV band transmission, a single crystal silicon membrane can besignificantly thicker (e.g., up to 10× thicker than other materials) andstill yield acceptable optical properties. Greater membrane thickness isadvantageous from a structural and mechanical standpoint. Thickermembranes are less prone to form local wrinkle defects (i.e., localslope variations). Therefore, in some mechanically advantageousembodiments, the membrane thickness is at least 50 nm.

FIG. 3A illustrates an isometric view of an exterior perimeter edge of amonolithic framed pellicle workpiece 301 delineated by dashed linewithin a SOI wafer 300 from which framed pellicle workpiece 301 is to bemachined, in accordance with some embodiments. As shown in FIG. 3, SOIwafer 300 includes a thin monocrystalline membrane material layer 305over a thick base, or “frame,” material layer 315, and an intervening(insulator) material layer 310 buried between material layers 305 and315. Frame material layer 315 may also be predominantly silicon, and insome advantageous embodiments, both frame material layer 315 andmembrane material layer 315 are substantially monocrystalline silicon(i.e., substantially pure silicon). Both base material layer 315 andthin material layer 305 may have substantially the same crystalorientation such that the two material layers are top and base layers ofone crystal. Although the crystal orientation may vary, in someadvantageous embodiments the crystal orientation is such that a front,or top, side surface of membrane material layer 305 is a {111} crystalfacet. As noted further below, such an orientation may facilitate ananisotropic etch of base material layer 315. A {100} crystal facet mayalso be suitable as the front side surface of membrane material layer305 (opposite frame material layer 315).

Either, or both of membrane material layer 305 and frame material layer315 may include specific impurity dopant species. Membrane materiallayer 305 may be doped with electrically active impurities for lowerelectrical resistivity or may only have intrinsic (unintentional)impurities for a high resistivity. Doping species and/or concentrationmay also be adjusted to optimize the optical properties, mechanicalproperties and/or chemical resistance of membrane material layer 305.Noting that single crystalline silicon becomes less susceptible tohydrogen etching with higher Boron concentrations, in some embodiments,membrane material layer 305 is doped with at least boron to improve themembrane's resistance to energetic hydrogen radicals than can begenerated on the reticle plan during EUV exposure in a lithographysystem.

In some embodiments, SOI wafer 300 may be received with one or moresensors 306 integrated into top material layer 305. As SOI wafer 300 maybe readily processed through nearly any IC fabrication flow, sensors 306may include one or more integrated circuit or microelectromechanicalsystems (MEMS) that has been fabricated directly on top material layer305 upstream of methods 200. Such integrated circuitry and/or MEMS maybe integrated into monolithic framed pellicle workpiece 301 as sensors306. Sensors 306, may, for example, sense pellicle membranethermomechanical or electrical properties, and/or sense environmentalconditions. In some embodiments, sensors 306 may sample over time one ormore properties such as, but not limited to, a pellicle membranetemperature, pellicle membrane acceleration, or pellicle membranestrain. In one specific example, sensors 306 include a piezoelectriceffect device that senses a change in electrical resistivity of thesingle crystal silicon membrane material as a function mechanicalstrain. Such a sensor may be incorporated on the membrane material 305,and associated circuitry (e.g., a wheatstone bridge, signal amplifier,etc.) could be also integrated onto the membrane material 305 (e.g.,within a peripheral region of monolithic framed pellicle workpiece 301).Sensors 306 may further comprise memory to store sensor data, and/or RFtelemetry circuitry to transmit sensor data, and/or programmable logiccircuitry. Sensors 306 may be powered directly, for example with asurface mount battery attached to monolithic framed pellicle workpiece301. Sensors 306 may also be powered by a photovoltaic fabricated on, ormounted to, monolithic framed pellicle workpiece 301 that may convertincident EUV radiation into stored charge. Alternatively, sensors 306may be powered through remote source coupled through either a conductiveroute (e.g., a through silicon via) between base material layer 315 andtop material layer 305, or through a near field inductive power couplerfabricated or mounted to monolithic framed pellicle workpiece 301.

As shown in FIG. 3A, frame material layer 315 has a base thickness T0.Base thickness T0 may vary and may only be 1 mm, for example, as afunction of the diameter of SOI wafer 300. Hence while membrane materiallayer 305 may be of thickness suitable as a pellicle membrane, basematerial thickness T0 may need to be supplemented, for example at block208 (FIG. 2A) where one or more bulk semiconductor wafers are bonded toa back side of an SOI wafer to reach a thickness desired for a pellicleframe. Any wafer-level thermo-compression bonding process may bepracticed, for example to directly bond a monocrystalline silicon waferto a back side of the frame material layer 315 (FIG. 3A). Such a bondingprocess may be repeated any number of times to reach a desired framematerial layer thickness (e.g., 2-3 mm). The bonded wafer stack may beof monocrystalline material layers (e.g., 2-3 layers) which mayadvantageously have the same crystal orientation, for example forconsistent mechanical properties that minimize warpage.

Insulator, or dielectric material, layer 310 also comprises silicon insome advantageous embodiments, but is an amorphous material layer at theinterface of membrane material layer 305 and frame material layer 315.In some such embodiments, dielectric material layer 310 is predominantlysilicon and oxygen (e.g., SiO₂). While dielectric material layer 310 mayhave any thickness, in some embodiments it is less than 100 nm, and mayeven be 10 nm, or less. In some embodiments where dielectric materiallayer 310 is a directly buried layer (e.g., where oxygen is implanted toa specific depth of a single silicon and annealed), both membranematerial layer 305 and frame material layer 315 will have the samecrystallinity (e.g., (111)) at the interfaces of dielectric materiallayer 310. In other embodiments where dielectric material layer 310 isindirectly buried (e.g., when an oxidized surface of a silicon wafer isbonded to another), membrane material layer 305 and frame material layer315 may, but need not, have the same crystallinity at the interfaces ofdielectric material layer 310.

Regardless of the crystal orientations of various material layers thatmight make up frame material layer 315, dielectric material layer 310and membrane material layer 305, the multi-layered laminate SOI wafer isstill to be considered monolithic in that the various material layerinterfaces are metallurgical with diffusion and/or molecular bondingacross the interfaces.

Returning to FIG. 2A, methods 200 continue at block 209 where the SOIwafer is cut down to the exterior dimensions of the pellicle frame. Theprocessing at block 209 may be performed with any waferscribe-and-break, laser ablation, or die saw machine, for example. Forsome embodiments, the SOI wafer is cut down to be rectangular with anarea of at least 100 mm-150 mm by 100 mm-150 mm (e.g., following thedashed lines outlining monolithic framed pellicle workpiece 301 in FIG.3A). Following block 209, the monolithic framed pellicle workpiece hasthe thickness and lateral dimensions suitable for a framed pellicle.Notably, block 209 need not be performed in the sequence illustrated inmethods 200 and is merely one possibility. In other embodiments, forexample, subsequent blocks of method 200 may be performed at thewafer-level, and the wafer subsequently cut down.

In alternative embodiments also illustrated in FIG. 2A, methods 200 mayinstead begin with receiving a dimensioned monolithic framed pellicleworkpiece at input 206. The workpiece for such embodiments has beenmachined upstream of methods 200 to have exterior dimensions suitablefor an outer perimeter edge of a monolithic framed pellicle. Forexample, the monolithic framed pellicle workpiece received at block 206may be substantially the same as the monolithic framed pellicleworkpiece generated by block 209 and have any of the propertiesdescribed above in the context of a SOI wafer (e.g., monocrystallinesilicon membrane and frame layers of desired area and thickness)received at input 205.

Methods 200 continue with blocks 210, 200 and 225 where the monolithicframe pellicle workpiece is coated with or more backside and front sidethin film capping layers, for example to arrive at the monolithic framedpellicle workpiece 301 illustrated in cross-section in FIG. 3B along theB-B′ line also shown in FIG. 3A. As illustrated in FIG. 3B, a backsidebarrier layer 318 is over, and in contact with, a back side of framematerial layer 315, which at this point has a desired frame thickness T1(e.g., 1-3 mm). Dielectric material layer 310 is between, and in contactwith, frame material layer 315 and membrane material layer 305. Membranematerial layer 305 has a thickness T2 (e.g., 15-150 nm). High emissivitylayer 330 is over, and in contact with, membrane material layer 220, anda protective layer 340 is over, an in contact with high emissivity layer330. While FIG. 3B illustrates one example, any number of other membranecapping layers can be incorporated onto either the front or back side insubstantially the same manner.

The various thin film layers illustrated in FIG. 3B may be formed in anyorder on a workpiece or at the wafer level prior to the wafer being cutdown into the workpiece. In the example illustrated in FIG. 2A, methods200 continue at block 210 where one or more thin film layers of barriermaterial are first formed upon the back side of the monolithic framedpellicle workpiece (opposite the membrane layer). Backside barriermaterial layer(s) formed at block 210 may advantageously protect theunderlying frame material layer. In some embodiments, barrier materiallayer is a silicon nitride layer (e.g., Si₃N₄) thermally grown in afurnace with ammonia or other suitable feed gas(es). Such a film mayhave high density and serve as a good barrier against reactions betweena silicon frame material and hydrogen radicals generated in the scannerenvironment. Alternatively, a silicon nitride (again comprising siliconand nitrogen but not necessarily in stoichiometric amounts) barriermaterial may be deposited using any suitable technique, such as, but notlimited to, low pressure chemical vapor deposition (LPCVD) or plasmaenhanced CVD (PECVD).

Methods 200 continue at block 220 where the high emissivity materiallayer is formed on the front side of the membrane material layer toimprove membrane heat dissipation during exposure to imaging radiation(e.g., EUV). The high emissivity material may be any material having ahigher emissivity than the membrane material, but in some exemplaryembodiments where the membrane material is silicon, the high emissivitymaterial is Ru. A Ru emissivity layer may have a thickness in the rangeof 2-5 nm, for example, and may be deposited by any of physical vapordeposition (PVD), ion beam deposition (IBD), or atomic layer deposition(ALD).

Methods 200 continue at block 225 where one or more protective materiallayers are deposited over the high emissivity material layer. Theprotective material is sacrificial and is to be subsequently removed. Assuch, the choice of material(s) may vary with one example being asilicon-based dielectric, such as a deposited silicon oxide (e.g., lowdensity with an RI<1.46). The protective material coating may bedeposited at a low temperature with LPCVD to a thickness ranging, forexample, from 0.5 μm to 1 μm.

As further illustrated in FIG. 2B, methods 200 continue at block 230where the monolithic framed pellicle workpiece is attached to a carrierwith the membrane material layer facing the carrier, and the protectivelayer in contact with the carrier, in preparation for backsideprocessing. Noting the monolithic framed pellicle workpiece isultra-flat (e.g., having been cut from a specular SOI substrate preparedunder stringent CMOS fabrication requirements), the carrier isadvantageously also ultra-flat. In some embodiments, the carrier is achemical mechanical polish (CMP) carrier assembly. The carrier assemblymay include, for example, an ultra-flat quartz or metal block. Bondingof the protective layer to the carrier can be accomplished through avariety of techniques, such as any commonly used in MEMS full-wafertemporary bonding processes. Examples include temporary bonding with aspin or spray adhesive or low temperature solder bonding at a pluralityof sites along the periphery of the monolithic framed pellicleworkpiece. Alternatively, the monolithic framed pellicle workpiece maybe affixed to the carrier by mechanical means, such as, but not limitedto, edge clamps, or screws.

Methods 200 continue at block 240 where a recess is milled into theframe material. In exemplary embodiments, bonnet polishing or a similarphysical milling technique is employed to fabricate the recess. Bonnetpolishing is often employed in ultra-high precision optical lensmanufacturing, for example. FIG. 4A is a cross-sectional view of amonolithic framed pellicle workpiece being machined from the backsidewith a bonnet polishing tool 415, in accordance with some embodiments.As shown in FIG. 4A, monolithic framed pellicle workpiece is mounted tocarrier 440. Bonnet polishing tool 415 is capable of precessed polishingand may be manipulated with a 7-axis CNC, for example. As shown in theexpanded view, bonnet polishing tool 415 has a primary spindle axis,from which the bonnet may precess by angle θ about a virtual pivot pointP. A membrane of radius R applies a controlled pressure at a spot onwhere frame material 315 (e.g., monocrystalline silicon) is polishedaway. The bonnet polishing tool 415 traverses the area that will retainonly the pellicle membrane to advance recess 450 progressively deeperinto frame material 315. Bonnet polishing tool 415 may employ any fluidslurry material 416 suitable for the frame material (e.g., silicon),such as, but not limited to, cerium oxide, ceria, or fumed silica.Bonnet polishing tool 415 is capable of milling a dimensionally preciserecess through the majority of the frame material thickness T1, andyielding a smooth surface (RMS roughness <10 nm) for subsequentprocessing that is more selective to the intervening dielectric materiallayer.

Although bonnet polisher milling may be a particularly advantageoustechnique, other techniques of forming the recess may be employed inalternative embodiments. For example, in some embodiments an ultrasonicmilling machine or a properly tooled high-precision vertical CNC millingmachine (e.g., ROBODRILL α-DiB5 commercially available from FANUCAmerica Corporation) is employed to grind a recess into the framematerial (e.g., silicon crystal). Additionally, if the appropriatecrystalline orientation is employed for a crystalline silicon framematerial layer, then anisotropic etching of the recess can beaccomplished by a chemical etchant (e.g., KOH, TMAH and other alkalinehydroxides like NaOH and LiOH).

FIG. 4B illustrates cross-sectional views of a monolithic framedpellicle workpiece evolving to include a pellicle structural frame, inaccordance with some embodiments. As shown, machining has stopped with apartial thickness T3 of frame material layer 315 remaining. With recess450 having a sufficient depth at this point, methods 200 (FIG. 2B) maycontinue at block 245 where additional backside machining (e.g., bonnetpolishing) may be conducted to mill vents and/or other features into aback side of the frame surrounding the recess.

FIG. 4C illustrates a plan view of a pellicle structural frame includingbackside features defined in monolithic framed pellicle workpiece, inaccordance with some embodiments. In this example, bonnet polishing oranother suitable milling technique is utilized to cut vent grooves 460in one or more of sides of the structural frame to allow for pressureequalization in vacuum environments (e.g., in scanner, actinicinspection metrology tooling, actinic pattern mask inspection tooling,etc.). Although vent grooves 460 are illustrated as straight through atransverse width of the peripheral frame material, a more circuitouspath may be similarly milled, if desired. Bonnet polishing and/ordrilling can be further employed to fabricate studs or detents 465 inthe back side surface of the frame material, for example to facilitatesubsequent alignment and/or mounting to mating features of a reticlesurface. Bonnet polishing and/or drilling may also be employed tofabricate a through via 470 into, and substantially through, framematerial 470. Through via 470 may be subsequently filled with aconductive material (e.g., solder, etc.) to serve as a conductive routebetween a reticle surface and an IC or MEMS device integrated into themembrane material layer, for example as described above. FIG. 4Dillustrates a cross-sectional view of monolithic framed pellicleworkpiece 301 along the C-C′ line illustrated in FIG. 4C, in accordancewith some embodiments. As shown, vent grooves 460 may have a depth lessthan frame thickness T1. Likewise, detents 465 may be any depth toprovide sufficient clearance for a mating stud on the surface of areticle. Through via 470 however extends completely through framematerial thickness T1, and also extends completely through dielectricmaterial layer 310. As shown, through via 470 stops within membranematerial layer 305, for example to intersect an unlanded via (notdepicted) that was previously fabricated in membrane material layer 305during the fabrication of an IC or MEMS device (e.g., as part ofintegrated sensor 306 in FIG. 3A). Through via 470 may extend further tobe landed on a device fabricated on the membrane material layer 305.Such a connection could facilitate measure of the membrane electricalproperties. For example, resistance of the membrane could be measuredand thus employed as a means for determining the continuity of themembrane (e.g., to detect if the membrane has ruptured). In still otherembodiments, for example where membrane material resistivity issufficiently lower through impurity doping, through via 470 mayintersect/connect directly to membrane material layer 305. In somespecific examples, a plurality of through vias 470 may be fabricated inorder to tie membrane material layer 305 to an electrical potential ofan underlying reticle to which it is attached.

Returning to FIG. 2B, methods 200 continue at block 250 where theinsulator layer of the workpiece is exposed at a bottom of the backsiderecess by selectively etching the remaining frame material thickness T3with any process offering adequate selectivity to the frame material(e.g., Si) over the dielectric material (e.g., SiO₂). In some exemplaryembodiments, reactive ion etch (RIE) is employed to remove the remainingsilicon frame material layer, and stop on the buried dielectric materiallayer. A dep/etch/dep Bosch type etch may be employed, for example, toarrive at the structure further illustrated in FIG. 4E. In someembodiments, the dielectric material layer 310 is also selectivelyremoved to expose a backside of membrane material layer 305, for exampleas further illustrated in FIG. 4F. RIE or any other etching technique(e.g., wet chemical) of sufficiently high selectivity to membranematerial layer 305 may be practiced. Notably, if the starting thicknessof dielectric material layer 310 is thin enough (e.g., <10 nm),reduction in membrane transmission will be minimal, and so dielectricmaterial can be left in contact with the membrane back side (i.e., theaforementioned operation can be omitted).

Returning to FIG. 2B with the dielectric material layer 310 now exposedand/or removed, methods 200 continue at block 255 where the carrier isremoved and the protective material stripped off of the high emissivitylayer. The protective may be removed using RIE or another suitable dryor wet chemical process. At block 260, barrier material may be depositedonto a back side of the membrane material. In some embodiments siliconnitride is again thermally grown on exposed silicon surfaces.Alternatively, a PECVD or LPCVD silicon nitride material may bedeposited over all exposed surfaces. Notably, other materials may bedeposited onto the back side of membrane material 205, in addition to,or instead of, silicon nitride. For example, a high emissivity materialcan be applied to the back side of the pellicle membrane material tofurther increase emissivity. Methods 200 continue at block 265 where themonolithic framed pellicle is thermally annealed. Annealing may relieveresidual stress in the membrane material and/or the surrounding framematerial. The anneal may be performed, for example, in-situ with barrierlayer formation (e.g., post SiN growth in the SiN furnace). The annealmay be performed in any appropriate ambient, such as, but not limitedto, forming gas (H₂:N₂). Methods 200 are then substantially completewith the monolithic framed pellicle at output 270 now ready to beaffixed to a reticle.

FIG. 5 illustrates a monolithic framed pellicle 501, in accordance withsome embodiments. As shown, a barrier material layer 518 has beenapplied to a back side of membrane material 305, rendering it a core ofa multi-layered material stack. In this example where dielectricmaterial 310 has been removed from the back side of membrane material305, dielectric material 310 remains only at the interfaces of framematerial 315 and membrane materials 305 around the periphery ofmonolithic framed pellicle 501. This remnant of dielectric material 310is indicative of monolithic framed pellicle 501 having been derived froma monolithic SOI staring material.

FIG. 6 illustrates a cross-sectional view of a pelliclized reticleassembly 601, in accordance with some embodiments. In this example, abackside of monolithic framed pellicle 501 is affixed to a top surfaceof reticle 115 by adhesive 610 (e.g. epoxy). In some embodiments wherean electrical connection is to be made between monolithic framedpellicle 501 and reticle 115, adhesive 610 may be a conductive material(e.g., solder). Any other technique known for attaching a pellicle to areticle may be practiced instead. As introduced above, reticle 115includes a feature pattern (not depicted in FIG. 6) that is to beimaged, for example through purely reflective optics. Pelliclizedreticle assembly 601 is ready for use, for example in a EUV lithographysystem. Although not depicted in FIG. 6, pellicle frame 315 may includeone or more structural features (e.g., detents or studs) to mate withone or more structural features (e.g., studs or detents) on reticle 115.

While certain features set forth herein have been described withreference to various implementations, this description is not intendedto be construed in a limiting sense. Hence, various modifications of theimplementations described herein, as well as other implementations,which are apparent to persons skilled in the art to which the presentdisclosure pertains are deemed to lie within the spirit and scope of thepresent disclosure.

It will be recognized that the invention is not limited to theembodiments so described, but can be practiced with modification andalteration without departing from the scope of the appended claims. Forexample the above embodiments may include specific combinations offeatures as further provided below.

In first examples, a monolithic framed lithography pellicle comprises asubstantially monocrystalline pellicle frame comprising silicon andenclosing a perimeter of an interior area, a substantiallymonocrystalline pellicle membrane comprising silicon and enclosing oneside of the interior area to define an interior cavity, and a dielectricmaterial layer between the pellicle frame and the pellicle membrane.

In second examples, for any of the first examples the pellicle framecomprises predominantly silicon, the pellicle membrane comprisespredominantly silicon, and the dielectric material layer comprisespredominantly silicon and oxygen.

In third examples, for any of the second examples the pellicle frame andpellicle membrane both consist of silicon and a minority impurityconcentration.

In fourth examples, for any of the third examples at least one of theimpurities in the pellicle membrane is boron.

In fifth examples, for any of the second examples the pellicle frame isa base layer of a crystal having a first crystal orientation. Thepellicle membrane is a top layer of the crystal having the first crystalorientation, and the dielectric material layer is a substantiallyamorphous material intervening between the base and top layers of thecrystal.

In sixth examples, for any of the fifth examples, the dielectricmaterial comprises predominantly silicon and oxygen.

In seventh examples, for any of the fifth examples a front side of thepellicle membrane, opposite the pellicle frame, is a {111} facet of thecrystal.

In eighth examples, for any of the first through seventh examples themembrane thickness less than 200 nm, the frame thickness is at least 3mm, and the interior area is at least 100 mm×100 mm.

In ninth examples, for any of the eighth examples the membrane thicknessis at least 50 nm.

In tenth examples, for any of the first through ninth examples thepellicle further comprises one or more polycrystalline or amorphous thinfilm material layers over a front side of the pellicle membrane,opposite the pellicle frame.

In eleventh examples, for any of the tenth examples the thin filmmaterial layers comprise a thin film material having higher emissivitythan monocrystalline silicon.

In twelfth examples, for any of the eleventh examples the thin filmmaterial layers comprise a Ru layer in contact with the front side ofthe of the pellicle membrane, the Ru layer having a thickness less than5 nm.

In thirteenth examples, for any of the first through twelfth examples,the pellicle further comprises one or more polycrystalline or amorphousthin film material layers covering at least a portion of the pellicleframe.

In fourteenth examples, for any of the thirteenth examples the thin filmmaterial layers comprise a dielectric material comprising silicon andnitrogen.

In fifteenth examples, for any of the first through fourteenth examplesthe dielectric material layer is over a back side of the pelliclemembrane, facing the cavity, and wherein the dielectric material overthe back side has a thickness less than 10 nm.

In sixteenth examples, for any of the first through fifteenth examplesthe pellicle frame comprises one or more vent grooves in a backsidesurface opposite the pellicle membrane, or the pellicle membranecomprises one or integrated sensors further comprising an integratedcircuit (IC) or microelectromechanical systems (MEMS).

In seventeenth examples, a pelliclized reticle assembly comprises alithography reticle including a feature pattern to be reflectivelyimaged upon a workpiece. The assembly comprises a monolithic framedpellicle, comprising a substantially monocrystalline pellicle framecomprising silicon and enclosing a perimeter of an interior area, asubstantially monocrystalline pellicle membrane comprising silicon andenclosing one side of the interior area to define an interior cavity,and a dielectric material layer between the pellicle frame and thepellicle membrane. A back side of the pellicle frame is to attach to amating surface of the reticle to contain the feature pattern within theinterior cavity.

In eighteenth examples, for any of the seventeenth examples the assemblyfurther comprises an adhesive between the back side of the pellicleframe and the surface of the reticle.

In nineteenth examples, for any of the seventeenth through eighteenthexamples the pellicle frame includes one or more first structuralfeatures to mate with one or more second structural features on thereticle.

In twentieth examples a method of fabricating a framed pelliclecomprises receiving monolithic workpiece comprising a substantiallymonocrystalline first material layer over a substantiallymonocrystalline second material layer with an intervening material layertherebetween. The method comprises attaching the monolithic workpiece toa carrier with a front side of the first material layer facing thecarrier. The method comprises subtractively machining a recess into thesecond material layer with a remainder of the second material layerframing a perimeter of the recess. The method comprises forming amembrane spanning the recess by the exposing a back side of theintervening material layer with an etchant that removes the secondmaterial selectively from the intervening material.

In twenty-first examples, for any of the twentieth examplessubtractively machining a recess into the second material layercomprises bonnet polishing the back side of the second material layer.

In twenty-second examples, for any of the twentieth through twenty-firstexamples further comprises at least one of removing the interveningmaterial layer, or depositing one or more polycrystalline or amorphousfirst material layers over a top surface of the first material layer, ordepositing one or more polycrystalline or amorphous second materiallayers over a bottom surface of the second material layer.

In twenty-third examples, for any of the twentieth through twenty-secondexamples the method further comprises removing the intervening materiallayer, depositing a layer comprising Ru over the top surface, anddepositing a layer comprising silicon and nitrogen over the bottomsurface.

In twenty-fourth examples, a method of fabricating a pelliclized reticleassembly comprises receiving the monolithic framed lithography pellicleof any of the first examples through fifteenth examples, receiving alithography reticle comprising a feature pattern to be imaged by alithography system, and mechanically coupling a back side of the framewith a surface of the reticle to contain the feature pattern within theinterior cavity of the monolithic framed lithography pellicle.

In twenty-fifth examples, for any of the twenty-fourth examplesmechanically coupling a back side of the frame with a surface of thereticle comprises curing an adhesive at an interface of the back side ofthe frame and the surface of the reticle.

However, the above embodiments are not limited in this regard and, invarious implementations, the above embodiments may include theundertaking of only a subset of such features, undertaking a differentorder of such features, undertaking a different combination of suchfeatures, and/or undertaking additional features than those featuresexplicitly listed. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A monolithic lithography pellicle, comprising: aframe comprising substantially monocrystalline silicon; a membranecomprising substantially monocrystalline silicon; and an amorphousmaterial between the frame and the membrane.
 2. The pellicle of claim 1,wherein the amorphous material comprises predominantly silicon andoxygen.
 3. The pellicle of claim 2, wherein the membrane comprises aminority impurity concentration.
 4. The pellicle of claim 3, wherein atleast one of the impurities in the membrane is boron.
 5. The pellicle ofclaim 1, wherein the frame has a first crystal orientation; and themembrane has the first crystal orientation.
 6. The pellicle of claim 5,wherein a front side of the membrane, opposite the frame, is a {111}crystal plane.
 7. The pellicle of claim 1, wherein: the membrane has athickness less than 200 nm; the frame has a thickness of at least 3 mm;and the frame encloses an interior area spanned by the membrane, and theinterior area is at least 100 mm×100 mm.
 8. The pellicle of claim 1,further comprising one or more thin film materials over a front side ofthe pellicle membrane, opposite the frame, wherein the thin filmmaterials have higher emissivity than monocrystalline silicon.
 9. Thepellicle of claim 1, further comprising a layer of predominantly Ru incontact with the front side of the of the membrane, opposite the frame.10. The pellicle of claim 9, wherein the Ru layer has a thickness lessthan 5 nm.
 11. The pellicle of claim 1, further comprising a dielectricmaterial layer comprising silicon and nitrogen on at least a portion ofthe frame.
 12. The pellicle of claim 11, wherein the dielectric materiallayer is on a back side of the pellicle membrane, proximal to the frame.13. A pelliclized reticle assembly, comprising: a lithography reticleincluding a feature pattern to be reflectively imaged upon a workpiece;and a monolithic lithography pellicle, comprising: a frame comprisingsubstantially monocrystalline silicon; a membrane comprisingsubstantially monocrystalline silicon; and an amorphous material betweenthe frame and the membrane.
 14. The pelliclized reticle assembly ofclaim 13, further comprising an adhesive between a back side of theframe and the reticle.
 15. The pelliclized reticle assembly of claim 13,wherein the frame comprises a first structural feature that interfaceswith a complementary second structural feature on the reticle.
 16. Amethod comprising: receiving a monolithic lithography pelliclecomprising: a frame comprising substantially monocrystalline silicon; amembrane comprising substantially monocrystalline silicon; and anamorphous material between the frame and the membrane; receiving alithography reticle comprising a feature pattern to be imaged by alithography system; and mechanically coupling the frame with the reticleto contain the feature pattern within an interior cavity of thepellicle.
 17. The method of claim 16, wherein mechanically coupling theframe with the reticle comprises curing an adhesive between a back sideof the frame and a surface of the reticle.
 18. The method of claim 16,further comprising depositing, upon the pellicle, a material layercomprising predominantly Ru over a front side of the pellicle membrane,opposite the frame, wherein the thin film materials have higheremissivity than monocrystalline silicon.
 19. The method of claim 16,further comprising depositing, upon at least a portion of the frame, adielectric material layer comprising silicon and nitrogen.
 20. Themethod of claim 16, further comprising reflectively imaging the featurepattern upon a workpiece.